Abstract

Objective: Autoantibodies to thyroglobulin are widely used as a serummarker for an autoimmune thyroiditis in the diagnosis of caninehypothyroidism. More than 50% of the hypothyroid dogs areTgAA-positive. TgAA are also detected in healthy and sick dogs with noevidence of thyroid dysfunction. The diagnostic and predictive value ofTgAA in these animals remains unclear. To answer this question weconducted a prospective study of TgAA-positive dogs. Material andmethods: Serum samples of 118 hypothyroid and of 2496 sick dogs wereinvestigated by ELISA. Results: TgAA prevalence was 58.6% and 6.25%,respectively. No gender predisposition was observed. However, certainbreeds showed an increased prevalence of TgAA. TgAA positive dogs weresignificantly younger than antibody negative ones. In a follow-up studyof 30 TgAA-positive dogs with hypothyroidism we observed, that all dogsbecame TgAA-negative within 2.5 year after the initial diagnosis. Thisindicates that TGAA-negative hypothyroid dogs are most likely in theendstage of an autoimmune thyroiditis. 156 out of 2496 sick dogs wereshown to be TgAA positive without any clinical sign of a thyroiddysfunction in the initial examination. 22.5% of these animalsdeveloped an overt hypothyroidism within two years. Clinical andscientific relevance: TgAA are a useful tool in the diagnosis of thyroiddysfunction and can be used as a marker to autoimmune thyroiditis.Whether and when these animals will develop an overt hypothyroidism iscertainly dependent on genetic, environmental and infectious factors andcannot be foreseen. Conclusion: Our data indicate that TgAA-positivedogs are on a higher risk to be affected by hypothyroidism.